Abstract
Isolation of crenarchaeol and its isomer from marine surface sediments, followed by ether cleavage and GC–MS characterization using supersonic molecular beam (SMB) ionization of the biphytanes formed, revealed that the crenarchaeol isomer comprises a tricyclic biphytane that is stereochemically different from the tricyclic biphytane of crenarchaeol. This isomeric tricyclic biphytane was also released from the crenarchaeol isomer in extant Thaumarchaeotal biomass. Reinterpretation of previously obtained 13C NMR data of the crenarchaeol isomer suggested that the cyclopentane moiety adjacent to the cyclohexyl moiety of the tricyclic biphytane of the crenarcheaol isomers possesses the unusual cis stereochemistry in comparison to the trans stereochemistry of all cyclopentane moieties in crenarchaeol. This stereochemical difference likely affects the packing of lipid membranes of Thaumarchaeota and therefore provides a biophysical explanation for the role of the crenarchaeol isomer in the TEX86 palaeothermometer based on fossilized Thaumarcheotal lipids.
Highlights
Glycerol dibiphytanyl glycerol tetraethers (GDGTs) form the core membrane lipids of many archaea and can be used as biomarker lipids
The resulting alkyl iodides were reduced to hydrocarbons with H2/PtO2 (Kaneko et al, 2011), which were analyzed with gas chromatography (GC) after on-column injection on an Agilent 7890B GC instrument and in splitless mode with gas chromatography-mass spectrometry (GC–MS) using an Agilent 7890A GC instrument equipped with a Agilent 5975C VL MSD detector
Crenarchaeol and the crenarchaeol isomer, isolated from Arabian Sea surface sediments, were subjected to ether cleavage with HI treatment followed by reduction of the formed BP iodides by H2/PtO2 (Kaneko et al, 2011; Lengger et al, 2014)
Summary
Glycerol dibiphytanyl glycerol tetraethers (GDGTs) form the core membrane lipids of many archaea and can be used as biomarker lipids. 20 eV SMB mass spectra of BPs I-IV released by ether cleavage of GDGTs. The m/z 400–600 range is expanded revealing the molecular ion and loss of the methyl group attached to the quaternary carbon atom of the cyclohexane moiety.
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